Seismic imaging of mantle transition zone discontinuities beneath the northern Red Sea and adjacent areas

Mohamed, A. A.; Gao, Stephen S.; Elsheikh, Ahmed; Liu, Kelly H.; Yu, Youqiang; Fat-Helbary, R. E.

doi:10.1093/gji/ggu284

Cited by 20 publications

(29 citation statements)

References 54 publications

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“…Previous studies have interpreted observations of depressed 660 in terms of increased water content in regions where subducted slabs are seen by increased shear wave velocities within the transition zone. Such strong depressions on the 660 in regions with subducting slabs have been seen beneath the Philippines [ Suetsugu et al , ], the western United States [ Cao and Levander , ], the Red Sea [ Mohamed et al , ], and Korea [ Lee et al , ]. Experiments on ringwoodite and pyrolite samples hydrated with 2 wt % water show an increased pressure of the dissociation of ringwoodite and a steeper Clapeyron slope [ Litasov et al , ; Ghosh et al , , Figure a].…”

Section: Discussionmentioning

confidence: 99%

Large‐scale mantle discontinuity topography beneath Europe: Signature of akimotoite in subducting slabs

Cottaar

Deuss

2016

JGR Solid Earth

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The mantle transition zone is delineated by seismic discontinuities around 410 and 660 km, which are generally related to mineral phase transitions. Study of the topography of the discontinuities further constrains which phase transitions play a role and, combined with their Clapeyron slopes, what temperature variations occur. Here we use P to S converted seismic waves or receiver functions to study the topography of the mantle seismic discontinuities beneath Europe and the effect of subducting and ponding slabs beneath southern Europe on these features. We combine roughly 28,000 of the highest quality receiver functions into a common conversion point stack. In the topography of the discontinuity around 660 km, we find broadscale depressions of 30 km beneath central Europe and around the Mediterranean. These depressions do not correlate with any topography on the discontinuity around 410 km. Explaining these strong depressions by purely thermal effects on the dissociation of ringwoodite to bridgmanite and periclase requires unrealistically large temperature reductions. Presence of several wt % water in ringwoodite leads to a deeper phase transition, but complementary observations, such as elevated Vp/Vs ratio, attenuation, and electrical conductivity, are not observed beneath central Europe. Our preferred hypothesis is the dissociation of ringwoodite into akimotoite and periclase in cold downwelling slabs at the bottom of the transition zone. The strongly negative Clapeyron slope predicted for the subsequent transition of akimotoite to bridgmanite explains the depression with a temperature reduction of 200–300 K and provides a mechanism to pond slabs in the first place.

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Section: Discussionmentioning

confidence: 99%

Large‐scale mantle discontinuity topography beneath Europe: Signature of akimotoite in subducting slabs

Cottaar

Deuss

2016

JGR Solid Earth

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“…We note that the introduction of a false low‐velocity anomaly into the MTZ during velocity corrections can produce an artificial uplift of the resultant d 660 depth and a thinner‐than‐real MTZ in order to account for the reduced velocities while maintaining the observed traveltimes. This scenario is discussed quantitatively at length in Mohamed et al [].…”

Section: Discussionmentioning

confidence: 99%

Passive rifting of thick lithosphere in the southern East African Rift: Evidence from mantle transition zone discontinuity topography

Reed

Liu

Chindandali³

et al. 2016

JGR Solid Earth

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To investigate the mechanisms for the initiation and early‐stage evolution of the nonvolcanic southernmost segments of the East African Rift System (EARS), we installed and operated 35 broadband seismic stations across the Malawi and Luangwa rift zones over a 2 year period from mid‐2012 to mid‐2014. Stacking of over 1900 high‐quality receiver functions provides the first regional‐scale image of the 410 and 660 km seismic discontinuities bounding the mantle transition zone (MTZ) within the vicinity of the rift zones. When a 1‐D standard Earth model is used for time‐depth conversion, a normal MTZ thickness of 250 km is found beneath most of the study area. In addition, the apparent depths of both discontinuities are shallower than normal with a maximum apparent uplift of 20 km, suggesting widespread upper mantle high‐velocity anomalies. These findings suggest that it is unlikely for a low‐velocity province to reside within the upper mantle or MTZ beneath the nonvolcanic southern EARS. They also support the existence of relatively thick and strong lithosphere corresponding to the widest section of the Malawi rift zone, an observation that is consistent with strain localization models and fault polarity and geometry observations. We postulate that the Malawi rift is driven primarily by passive extension within the lithosphere attributed to the divergent rotation of the Rovuma microplate relative to the Nubian plate, and that contributions of thermal upwelling from the lower mantle are insignificant in the initiation and early‐stage development of rift zones in southern Africa.

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“…The left-lateral strike-slip Dead Sea Transform continues to the Aqaba fault zone at the northeastern boundary. On the eastern side, the Red Sea represents an active extension zone dividing the African and Arabian plates at a variable extension rate, which increases from the north (∼ 5.6 mm yr −1 ) to the south (14 mm yr −1 ; McClusky et al, 2003). This active environment produces high and continuous seismic activity in the region (Fig.…”

Section: Tectonic Settings and Seismicity Of Egyptmentioning

confidence: 99%

“…These studies show that the coverage of the territory of Egypt based on seismic methods is very heterogeneous. While the areas adjoining the Red Sea and Mediterranean are well studied Hosny and Nyblade, 2016;Mohamed et al, 2014), the data for the central, western, and southern parts are sparse. Several important questions remain unresolved.…”

Section: Introductionmentioning

confidence: 99%

“…Such an integrative geophysical study is applied to the study area for the first time; this was made possible due to the availability of new data after establishing in 1997 the Egyptian National Seismic Network (ENSN), which provided the input for new receiver functions and tomography models of the Egyptian lithosphere (e.g., El Khrepy et al, , 2016Abdelwahed et al, 2013;Hosny and Nyblade 2016;Mohamed et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Density structure and isostasy of the lithosphere in Egypt and their relation to seismicity

2018

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Abstract. A joint analysis of the new satellite-terrestrial gravity field model with recent data on the crustal structure and seismic tomography was conducted to create an integrative model of the crust and upper mantle and to investigate the relation of the density structure and the isostatic state of the lithosphere to the seismicity of Egypt. We identified the distinct fragmentation of the lithosphere of Egypt in several blocks. This division is closely related to the seismicity patterns in this region. The relatively dense and strong lithosphere in the Nile Delta limits the seismic activity within this area, while earthquakes are mainly associated with the boundaries of this block. In the same way, the relatively strong lithosphere in the Isthmus of Suez and northern Mediterranean prevents the Gulf of Suez from opening further. The central part of Egypt is generally characterized by an increased density of the mantle, which extends to the Mediterranean at a depth of 100 km. This anomaly deepens southward to Gilf Kebir and eastward to the Eastern Desert. The average density of the crystalline crust is generally reduced in this zone, indicating the increased thickness of the upper crust. The low-density anomaly under the northern Red Sea is limited to 100-125 km, confirming the passive origin of the extension. Most of the earthquakes occur in the crust and uppermost mantle in this structure due to the hot and weak upper mantle underneath. Furthermore, an asymmetric lithosphere structure is observed across the northern Red Sea. The isostatic anomalies show the fragmentation of the crust of Sinai with the high-density central block. Strong variations in the isostatic anomalies are correlated with the high level of seismicity around Sinai. This tendency is also evident in the northern Red Sea, east of the Nile Valley, and in parts of the Western Desert.

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Seismic imaging of mantle transition zone discontinuities beneath the northern Red Sea and adjacent areas

Cited by 20 publications

References 54 publications

Large‐scale mantle discontinuity topography beneath Europe: Signature of akimotoite in subducting slabs

Large‐scale mantle discontinuity topography beneath Europe: Signature of akimotoite in subducting slabs

Passive rifting of thick lithosphere in the southern East African Rift: Evidence from mantle transition zone discontinuity topography

Density structure and isostasy of the lithosphere in Egypt and their relation to seismicity

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